Axel, After I made my post, I re-read yours, and I realized I had slightly missed the point of your question. You might want to read the "white paper" on the Jensen transformer website, where they cover the complex issue of loading very well and describe the use of a Zobel network to attain flat fequency response. I've never used a SUT, so thankfully I have not needed to think it thru in as much detail as you have done. I would not have thought that the Ortofon or any other similar MC would be "happy" with only a 10-ohm load, but you have done the listening, whereas I have not. If you have a 47K resistance on the secondary side of you SUT, that will always reflect a 47-ohm impedance to the cartridge (if the tranny has a 10:1 ratio). So if you put 100 ohms on the primary side, the cartridge would "see" 100R in parallel with 47R (i.e., very low). For 10R, the net Z gets even lower. All of this interests me because I have a newly acquired Orto MC7500 direct-driving my phono section. By all accounts these Ortos like about 500 ohms. As regards bandwidth, does not the inductance of the SUT itself have much more effect than the inductance of the cartridge windings? Dunno. |
That sounds so impossibly high that I agree it MUST be an error. There's just not enough wire in there to generate that much inductance. I will bet that they meant to write "micro-" Henries, not "milli-". Even that much seems a tad high. Of course, I am only guessing. |
Axelwahl, You originally asked about inductance, not impedance. This naturally led some people to ask why you wanted that information, since the proper loading of your cartridge is easiest to calculate based on the square of its turns ratio of the SUT you are using, if you know the desired load. For example, if you want the cartridge to "see" a 100-ohm load (a reasonable guess for a cartidge with a 4-ohm internal impedance, altho I know the Ortofon likes to see a higher value), and if your SUT has a turns ratio of 10:1, then the proper value of the load resistor on the secondary side of the SUT is 10,000 ohms. (The square of the turns ratio = 10^2 = 100; 100*100 ohms (the desired load) = 10,000 ohms.) If you want the Ortofon to see 500 ohms, then you need a 50K ohm load resistor. Maybe you know all this, but the fact remains that inductance of the cartridge is not needed to make this calculation. Folks were trying to help you. |
Sorry, you are correct about my math error. 470 not 47. Much better.
Your findings as to the sonic differences between loading the PW with NO trannie vs loading it either on the primary side or the secondary of a SUT are quite fascinating, and I don't know of anyone else who uses a SUT and loads the cartridge on the primary side. Tonight I have been listening to my MC7500, father of your PW, with no SUT and a 100R load. I don't hear any particular tonal imbalance, but the sound seems a tad closed in compared to my Koetsu Urushi (but tonearm and mat and tt are also different so not a good piece of data). Nevertheless, I am prepared to try 500R next, as this was advice I got from the previous owner of the MC7500. Can you once again describe the circuit you are happiest with? Reading two posts up from this one, I think you are using a 13R resistor on the primary side and a 47K resistor on the secondary side of your SUT, so that the PW sees 13 in parallel with 47 to give about 10R. Is that correct? |
Axel, Now it is YOU who have misunderstood ME. You wrote, "So, the SUT secondary "sees" the 47k input-impedance of the phono-pre! If you put -another- 47k R (as you implied)". No, I did not mean to imply nor did I think that you have two 47K resistors in parallel on the secondary, I did mean to ask whether the sole parallel resistance on the secondary side of your SUT is the 47K-ohm input Z of the phono section. That's what I wrote. Your whole paragraph on the undesirable result of paralleling two 47K resistors is beside the point. I just wanted you to summarize what resistances you have and where they are in your circuit to give you the sound you like from your PW.
And thank you for the advice on SUT installation, but there is no way I am going to be buying and installing a SUT, when my phono pre has oodles of gain and sounds great. I am just interested in your findings. |
I really think it's quite interesting and unexpected (to me) that with pre-loading of a SUT, the optimal impedance for the PW seems to be about 10 ohms net, whereas, as you say, without the SUT the PW seems to like 500 to 1000 ohms net. I am not close-minded about using a SUT; this is the first report that suggests there could be an advantage notwithstanding any need for extra gain. |
Thanks very much, Dave. I bookmarked that thread for future reference. But in your experience with primary vs secondary loading does it often occur that the optimal net load for a given cartridge, when you load the primary of the SUT, is radically different from its optimal loading when there is NO SUT or when the load is in the SUT secondary? I can see how that could happen due to introduction of the SUT, thanks to the post you cited. |
I learned something. To paraphrase Gertrude Stein, a SUT is not a SUT is not a SUT. |
Axel, No one is arguing with your logic, and I am not foxed. I will leave it to Dave (Intactaudio) to comment on the second half of your post. Dave knows more about transformers than both of us. I did learn something from your story, so thanks. |
Axel, I am often vexed by the same phenomenon-reviewers who comment on the "sound" of a SUT without regard to the myriad of other parameters that affect the result. Particularly egregious is the "SUT shoot-out" type of review, where many different SUTs are compared using the same cartridge and the exact same loads, often without regard to the differences in turns ratio, let alone other less important factors. The result is worthless information, but it fills pages in a magazine. |
Jonathan, You are correct. I just did not want to go into great detail on Dave's qualifications. |
Thanks for your input, Dave. |
Dear Axel, Intactaudio is a professional in the use of transformers, autoformers, chokes, etc, in audio. He is highly respected on other internet forums for his knowledge and unbiased advice. Rather than leaving in a huff, you might be better served by considering that what he has written in response to your posts is most likely correct. Then you can learn something new, which is what we are all here for. No one, including Dave, is saying that your particular choice of a topology for your cartridge and your SUT does not sound excellent. |
Axel, To me, the "minimum impedance" spec given by the cartridge maker is not the same as the optimal impedance. Can you name any cartridges where two different impedances are suggested, one for SUT, one for no SUT? In my very limited experience as an owner of high-end LOMCs, I have not seen that. This is not a challenge to your integrity or your perspicacity, just a question.
Larryi, The point you are making is exactly the same one I was trying to make with Axel, when this thread was in its infancy. His finding is interesting, indeed. His response to that question is what got us rolling in the current direction (pun intended). |
